The proposed work continues our studies of mechanisms of hypertension in coarctation of the aorta using a unique experimental canine model in which coarctation is induced in the neonatal period. Our previous studies demonstrated that baroreflex sensitivity is normal in this model in contrast to other hypertensive stages in which it is depressed. We also showed that carotid sinus diameter was greatly increased in these animals. In the current investigation we are determining whether the preservation of baroreflex sensitivity is related to enlargement of the carotid sinus, which may only occur in all growing animals with hypertension or to some peculiar effect of aortic coarctation. The locus of the adaptation in baroreflex function is being examined by making direct recordings of carotid sinus nerve activity. The problem of paradoxical hypertension following surgical correction of aortic coarctation is being studied by monitoring blood pressure, cardiac output and baroreflex sensitivity after repair of the coarctation to see if these animals demonstrate the same phenomenon as humans.